Mutant Butterflies At Fukushima Nuclear Plant

Genetic mutations have been found in three generations of butterflies near Japan's tsunami-hit Fukushima nuclear plant.

The abnormalities have raised fears that radiation may have spread to other species, including humans.

Around 12% of the pale grass blue species exposed to nuclear fallout as larvae immediately after the disaster had abnormalities.

These included smaller wings and damaged eyes, researchers said.

The insects were mated in a laboratory well outside the fallout zone and 18% of their offspring displayed similar problems.

That figure rose to 34% in the third generation of butterflies, said Joji Otaki, associate professor at Ryukyu University in Okinawa, Japan.

The researchers also collected another 240 butterflies in Fukushima in September last year, six months after the disaster.

Abnormalities were recorded in 52% of their offspring, which was "a dominantly high ratio", Mr Otaki said.

Mr Otaki said the high ratio could result from both external and internal exposure to radiation from the atmosphere and in contaminated food.

The results of the study were published in Scientific Reports , an online research journal from the publishers of Nature.

Mr Otaki later carried out a comparison test in Okinawa exposing unaffected butterflies to low levels of radiation. The results showed similar rates of abnormality, he said.

"We have reached the firm conclusion that radiation released from the Fukushima Daiichi plant damaged the genes of the butterflies," Mr Otaki said.

The tsunami of March 2011 knocked out cooling systems at the Fukushima Daiichi nuclear power plant .

It caused three reactors to go into meltdown in the world's worst atomic disaster for 25 years.

The findings will raise fears over the long-term effects of the leaks on people who were exposed in the days and weeks after the accident.

Radiation spread over a large area and forced thousands to evacuate.

There are claims that radiation affected successive generations of people living in the atomic bomb-hit cities of Hiroshima and Nagasaki.

But Mr Otaki warned it was too soon to jump to conclusions, saying his team's results could not be directly applied to other species.